The present invention relates to a permanent magnet type rotating electric machine and, more particularly, to a permanent magnet type rotating electric machine in which permanent magnets are embedded in a rotor core.
In a three-phase AC induction motor, the rotation speed is inversely proportional to the number of phases. Thus, two phases are preferable for high-speed rotation. In a two phase interior permanent magnet (IPM) motor rotating at a high speed, the centrifugal force applied to the permanent magnets increases the stress applied to the rotor core. When the rotor core is thin at a portion between the permanent magnets and the outer circumferential surface of the rotor core, stress may break the rotor core.
The thickness of the rotor core may be increased at the portion between the permanent magnets and the outer circumferential surface of the rotor core to prevent breakage of the rotor. However, this will lower the torque. Further, the rotor core will be enlarged. This will increase the size of the IPM motor.
The IPM motor may have substantially two poles in which each pole corresponds to a plurality of permanent magnets so that centrifugal force acting on the individual permanent magnets is reduced. However, this will increase leakage flux and lower the torque.
Japanese Laid-Open Patent Publication No. 2012-110214 describes a brushless motor provided with a rotor that includes a plurality of magnet pole portions arranged in the circumferential direction of the rotor core to limit demagnetization and to increase the torque and improve the rotation performance. An N-pole magnet is embedded in each magnet pole portion. The rotor core includes a core pole portion that functions as an S-pole between the magnet pole portions that are adjacent in the circumferential direction. Gaps extend between the core pole portions and the magnet pole portions. The gaps between the magnet pole portions and the core pole portions extend toward the radially outer side of the magnets.